1. Field of the Invention
The present invention relates to a valve timing control apparatus for a valve timing adjustment mechanism that changes timing of opening and closing an intake valve or an exhaust valve.
The present invention also relates to a valve timing control apparatus that is capable of learning a width of a dead zone of a control signal, wherein a hydraulic variable valve mechanism is unable to respond to the control signal when the signal is within the dead zone.
The present invention also relates to a valve timing control apparatus for an internal combustion engine, the valve timing control apparatus being capable of learning a hold control amount required for maintaining actual value of the valve timing at a constant state.
2. Description of Related Art
The above valve timing adjustment mechanism includes an output-side rotor, a cam-side rotor, a hydraulic pump, and a control valve. The output-side rotor is rotatable synchronously with an output shaft of an internal combustion engine, and the cam-side rotor is rotatable synchronously with a camshaft that opens and closes an intake valve or an exhaust valve. The hydraulic pump supplies hydraulic oil such that one of the above rotors rotates relative to the other one of the rotors. The control valve controls speed of the relative rotation by controlling the supply of hydraulic oil in accordance with a drive command signal outputted by a control device (see JP-A-2003-254017).
In the adjustment mechanism, in a hold case, where the relative rotation speed is zero and thereby the rotational position of the one of the rotors relative to the other is maintained, slight change of the drive command signal hardly changes speed of the relative rotation. However, when the change of the drive command signal exceeds a certain amount, the relative rotation speed suddenly changes. As above, a change amount of a drive command signal from a first value to a second value is referred as a “dead zone width”. For example, when the drive command signal is at the first value, the relative rotational position is under the hold state, and when the drive command signal is changed from the first value to become the second value, the relative rotation speed starts changing sharply.
The dead zone width changes depending on individual differences of the adjustment mechanisms or variations with time of the adjustment mechanisms. Moreover, when temperature of hydraulic oil is lower, viscosity of hydraulic oil becomes higher. Thereby, the dead zone width of each of the adjustment mechanisms widely changes with temperature. As a result, in a case, where relative rotation speed is controlled by operating the control valve through the drive command signal, the resulting relative rotation speed may widely change depending on a magnitude of the dead zone width even when the same drive command signal is given. Thus, the computation of the drive command signal in consideration of the dead zone width at the time of the operation is important for accurately controlling the relative rotation speed. If the relative rotation speed is accurately controlled, it is possible to minimize hunting, and also to improve responsivity by quickly rotating one of the rotors relative to the other to a desired position. In other words, it is possible to quickly adjust timing of opening and closing the intake valve or the exhaust valve to desired timing.
JP-A-2003-254017 proposes to execute an inching control that alternately executes a forcible drive control and a stop control for predetermined durations when a difference between an actual relative rotational position and a target position is large. The forcible drive control forcibly drives the relative rotation speed to the maximum, and the stop control stops the relative rotation of the rotors. However, is it very difficult to adjust inching cycle, a forcible drive duration, a rotation stop duration in order to improve responsivity if the inching control is put into practice.
Recently, the more and more internal combustion engines mounted on the vehicles are provided with hydraulic variable valve timing apparatuses that change valve timing of opening and closing the intake valve or the exhaust valve of the engine in order to increase the output, to improve the fuel efficiency, and to reduce exhaust gas emission. The hydraulic variable valve timing apparatus computes a control duty for controlling a hydraulic control valve, which adjusts drive oil pressure, based on a difference between target valve timing and actual valve timing, and the hydraulic control valve is driven based on the computed control duty such that flow amount (oil pressure) of hydraulic oil supplied to an advance chamber and a retard chamber of the variable valve timing apparatus is changed, and thereby the valve timing is advanced or retarded.
As shown in JP-A-2001-164964, JP-A-2003-336529, and JP-A-2007-107539, in the hydraulic variable valve timing apparatus, a change characteristic (response characteristic) of the valve timing variable speed relative to change of the control duty of the hydraulic control valve is non-linear, and there is a dead zone, in which change of valve timing relative to change of the control duty is very slow. Thus, it is known that responsivity of the variable valve timing control may remarkably deteriorate disadvantageously when the control duty stays within the above dead zone.
Thus, in JP-A-2003-336529 and JP-A-2007-107539, in order to learn the width of the dead zone, the control signal is oscillated by an amplitude greater than a magnitude of a possible dead zone width. Then, while the actual valve timing oscillates around target value (a center of the dead zone), the amplitude of the control signal is gradually reduced. Then, the dead zone width is learned based on the amplitude of the control signal when the oscillation of the actual valve timing stops. Also, under a state, where the actual valve timing is maintained unvibrated at the target value, the amplitude of the control signal is gradually increased. The dead zone width is learned based on the amplitude of the control signal at a time when the actual valve timing starts vibrating. When the target value changes during the variable valve timing control, the control signal is offset-corrected based on the learned value of the dead zone width.
However, the dead zone width learning methods described in JP-A-2003-336529 and JP-A-2007-107539 require trouble of adjusting a cycle and the amplitude for oscillating the control signal disadvantageously.
Recently, more and more internal combustion engines mounted on the vehicles are equipped with hydraulic variable valve mechanisms that change valve timing (opening-closing timing) of an intake valve and an exhaust valve of the engine in order to improve output, to improve fuel efficiency, and to reduce exhaust gas emission. The hydraulic variable valve mechanism as described in JP-A-2007-224744 and JP-A-2004-251254, a control amount (control duty) of a hydraulic control valve for controlling oil pressure is computed based on a feed-back correction amount and a hold control amount (hold duty). The feed-back correction amount is determined based on a difference between the target value and the actual valve timing, and the hold control amount corresponds to an amount that is required to maintain the actual valve timing under a constant state. By driving the hydraulic control valve based on the control amount to change a flow amount (oil pressure) of hydraulic oil supplied to an advance chamber and a retard chamber of the variable valve timing apparatus, valve timing is advanced or retarded. In the above operation, the hold control amount is learned in consideration of that the hold control amount may change depending on manufacturing variations and variation with time of the variable valve mechanism and the hydraulic control valve.
Because fluidity (viscosity) of hydraulic oil and a clearance between components of the variable valve mechanism change with oil temperature, the hold control amount required for maintaining the actual valve timing at the constant state changes with oil temperature.
As shown in JP-A-2000-230437, a hold control amount is learned for each of multiple temperature sections.
However, in the system that learns the hold control amount of each of the multiple temperature sections, in a case, where the hold control amount has been learned in a certain temperature section and a hold control amount in the other temperature section different from the above certain section has not been learned, the hold control amount learned in the certain temperature section is not able to be used for executing the variable valve timing control in the other temperature section. Thus, the accuracy in performing the variable valve timing control may deteriorate. Furthermore, because the frequency of executing the learning operation for learning the hold control amount is different for the different temperature section. As a result, accuracy in the learning operation of the hold control amount may become lower for the temperature section having the lower frequency. Therefore, the accuracy in the variable valve timing control may deteriorate disadvantageously.